1. Field of the Invention
This invention relates to variable reflective and variable transmission layers and more particularly to an improved electrochromic device with superior variable reflective and variable transmission properties.
2. Background of the Related Art
Electrochromic devices operate in a manner similar to the operation of a battery. In a battery, electrons or ions are stored in layers of materials commonly referred to as battery plates. The ions are available to move to perform work when connected to an external electrical circuit.
An electrochromic device has an electron/ion storage layer and an electron/ion active layer. In the electrochromic device, the charge state of the active layer affects the optical properties of the electrochromic device. When an ionic species (+) is drawn into the active layer by an applied voltage the active layer of the electrochromic device becomes opaque. When the voltage is reversed, the ionic species (+) moves away from the active layer to the storage layer and the active layer of the electrochromic device becomes clear.
An electrochromic device is made of several layers of materials with each layer being capable of transmitting light in the visible spectrum. Since the electrochromic device must be capable of transmitting light in the visible spectrum, each of the several layers is made appropriately thin.
The active layer of the electrochromic device which stores the ions and changes optical properties is usually a transition metal oxide such as tungsten trioxide (WO3) or nickel oxide (NiO). Tungsten based devices dominate research since the optical properties are more suited for solar spectral abatement. The WO3 film is dominated by dense highly columnar regions and an intermolecular void network. With a small negative voltage applied to the top electrode closest to the WO3 film, positively charged ions diffuse into these voids from the ion storage layer through the electrolyte. This changes the stoichiometry and optical characteristics darkening the electrochromic film. The amount of light transmitted through the film can be adjusted by controlling the voltage applied to the device or the length of time the voltage is applied to the device. The film can then be discharged and made transparent by reversing the voltage.
The other critical layer to the electrochromic device is the ion-conductor layer (analogous to the electrolyte in a battery). The ion conductor layer must be able to pass ions into the adjoining electrochromic layer yet suppress electron transport. Organic polymers as well as solid state electrolyte materials have been successfully demonstrated as ion conductor layers. Organics are relatively inexpensive, easy to apply, and flexible. Unfortunately, organic emulsions are the most sensitive to ultraviolet light and weathering degradation.
Solid state electrolytes such as tantalum pentoxide Ta2O5, magnesium fluoride MgF, or lithium nitride Li3N can be more difficult to apply but are more stable and offer better durability properties necessary for large scale applications such as windows or the like.
The final layer used in the electrochromic device is the ion storage layer. The ion storage layer may be fabricated from materials such as vanadium pentoxide V2O2.
Electrodes for the electrochromic device may be either of a transmissive electrode or a reflective electrode. Although many types of transparent conductors are available, the most popular material for transmissive electrode is indium-tin-oxide (ITO). Although many types of reflective conductors are available, the most popular materials for reflective electrode are silver and aluminum.
U.S. Pat. No. 4,110,015 to Reddy discloses an improved electrolyte for use in electrochromic devices. These electrolytes are prepared by the incorporation of a lithium salt in a solvent selected from dimethylsulfite, nitromethane, and sulfolane.
U.S. Pat. No. 4,253,742 to Morita discloses an electrochromic display cell comprising a display electrode, a counter electrode spaced from and facing the display electrode and an electrochromic layer deposited on the display electrode, and a solid electrolyte layer conductive to lithium ion disposed between the electrodes. The solid electrolyte layer is formed from materials selected from the group consisting of Li3N, Li2+xC1xe2x88x92x BxO3, Li4+x Si1xe2x88x92x PxO4 and Li5+xAg1xe2x88x92x SixO4 where 0 less than x less than 1.
U.S. Pat. No. 4,491,392 to Elmer et al. discloses an electrochromic device comprising a solid electrolyte wherein the electrolyte consists of porous glass impregnated with a solid ion-conductive compound such as an alkali metal salt.
U.S. Pat. No. 4,687,560 to Tracy et al. discloses a method of synthesizing electro-optically active reaction products from a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.
U.S. Pat. No. 5,260,821 to Chu et al. discloses an electrochromic system which comprises layers of solid/materials deposited on glass or another substrate. The solids function in an atmosphere that can be dry. One layer is preferably Li3AlF6 and conducts positive lithium ions. Another layer is a counterelectrode. The counterelectrode is improved to the extent that it can reversibly accept ions from and donate them to the ion conductor while remaining extensively transparent. The counterelectrode can be LixTiOy, (Li2O)mWO3)n(Sb2O3), or (Li2O)m(WO3)nxe2x80x94(CeO2)o.
U.S. Pat. No. 5,404,244 to Van Dine et al discloses the invention which provides for the simplified production of chromogenic devices including relatively large scale devices in panel form. One or more of the layers of the invention are formed from heated, hydrolyzed gel reaction product of one or more dissolved organo-inorganics, such as alkoxides, which may be metallic. The invention includes an ion-conducting layer which comprises a lithium based ceramic material containing residual organic impurities.
U.S. Pat. No. 5,659,417 to Van Dine et al. discloses electrochromic devices applied to a substrate including an electrochromic electrode layera, a counterelectrode layer and an ion-conducting layer sandwiched between those two layers and electrically isolating them from each other. The ion-conducting layer is substantially uniform across the substrate and comprises an inorganic superstructure with associated organic material and with a microstructure which facilitates the transfer of ions. Methods for producing these devices are also disclosed including depositing the ion-conducting layer on the substrate in the form of a solution, and effecting gelation of that solution.
U.S. Pat. No. 5,663,829 to Lefrou et al. discloses an electrochromic system comprising a transparent electrically conducting film, a film of a cathodic electrochromic material, which is capable of reversibly inserting M+ cations of type H+ or Li+, an electrolyte film, counter-electrode film made of an anodic electrochromic material, and a second electrically conducting film. The structure having a barrier film interposed between the electrolyte and the counter-electrode. The barrier film is open to the diffusion of the M+ cations and is constituted of the following materials selected from the group consisting of oxides of metals of Group VB of the Periodic Table, mixtures of these oxides, CeF3, Sb2 O3, HUP (hexauranylphosphate), Cr2O3, ZrO2, and an ion conductor material of Li3N, LiTaO3, LiAlF4, Li3PO4, LiBO2 or LiNbO3.
U.S. Pat. No. 5,666,771 to Macquart et al. discloses an invention which concerns an electrochromic pane comprising a principal functional film constituted of a material which under the effect of an electric current is capable of reversibly inserting cations and which has characteristics of coloration and/or transmission in certain wavelengths of electromagnetic radiation that differ for its inserted and deinserted states. The principal functional film has a quasi-columnar structure, with axes of growth of the columns parallel to straight lines contained within a dihedron, the opening of which is less than 20 degrees and the bisector plane of which makes an acute angle with the substrate.
U.S. Pat. No. 5,757,537 to Ellis, Jr. et al. discloses an electrochromic device which may be used for large surface area applications. The devices utilize optical tuning to minimize optical interference between layers of the structure and to maximize uniform optical transparency. Optical tuning also enables transparent conductive oxide layers to be replaced by thin conductive metal layers, thereby reducing the overall thickness of these devices and facilitating the manufacturing process.
U.S. Pat. No. 5,780,160 to Allemand et al. discloses electrochromic devices and processes for preparing the same which are provided which do not require a separate process step of ion intercalation by employing an electrochromically-inert reducing or oxidizing additive in the electrochemically active material or the electrolyte of the electrochromic devices.
Although the aforementioned patents have made advancement to the electrochromic art, the aforementioned patents have not provided electrochromic devices suitable for large scale in a wide variety of uses and applications.
Therefore, an object of this invention is to provide an improved electrochromic device with superior properties than heretofore known in the art.
Another object of this invention is to provide an improved electrochromic device having a rapid response heretofore unknown in the electrochromic art.
Another object of this invention is to provide an improved electrochromic device which may be manufactured on a commercial basis at a reasonable cost.
Another object of this invention is to provide an improved electrochromic device which is reliable and durable enabling the improved electrochromic device to be used in hostile environments.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention with in the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment of the invention.
A specific embodiment of the present invention is shown in the attached drawings. For the purpose of summarizing the invention, the invention relates to an improved method and an improved electrochromic device comprising a substrate and a first conductive layer located on the transparent substrate. An ion storage layer is located on the first conductive layer. An electrolyte layer is located on the ion storage layer with an active layer being located on the electrolyte layer. A second conductive layer is located on the active layer.
In a more specific embodiment of the invention, the improved electrochromic device includes conductive bus bars located on the first conductive layer and located on the transparent substrate. A hermetic layer is bonded to the transparent substrate for sealing the electrochromic device of the present invention.
In one embodiment of the invention, the substrate is substantially transparent. In a more specific example of the invention, the first conductive layer located on the transparent substrate is indium-tin-oxide (ITO).
In another embodiment of the invention, the ion storage layer located on the first conductive layer is vanadium pentoxide (V205). The electrolyte layer located on the ion storage layer is an inorganic solid state electrolyte comprised of lithium phosphate (Li3PO4).
In one embodiment of the invention, the active layer located on the electrolyte layer is a transition metal oxide. In another example of the invention, the active layer located on the electrolyte layer is selected from the group consisting of tungsten trioxide (WO3) and nickel oxide (NiO). Preferably, the active layer located on the electrolyte layer is tungsten trioxide (WO3).
In still a further embodiment of the invention, the second conductive layer located on the active layer is transparent. In another example of the invention, the second conductive layer located on the active layer is transparent indium-tin-oxide (ITO). In another example of the invention, the second conductive layer located on the active layer is reflective. In another example of the invention, the second conductive layer located on the active layer is reflective aluminum (Al).
The invention is also incorporated into the method of forming the improved electrochromic device wherein at least one of the layers is deposited by vacuum deposition. In another example of the invention, at least one of the layers is deposited by plasma enhanced chemical vapor deposition (PECVD).
The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description that follows may be better understood so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject matter of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention.